Many different substances have been used as dental impression materials, each having its own advantages and disadvantages. An impression material must undergo a transformation, while in the mouth, from a viscous liquid to a rubbery solid. While factors such as taste, odor, toxicity, viscosity, cure speed, ease of demolding and strength after cure are all important, accuracy is of paramount concern. An impression material must accurately replicate the shape, size, and relative locations of both hard and soft tissues within the mouth. After cure, the impression must enable casting ("pouring") of an accurate model. The model usually is a plaster of Paris "stone" prepared from an aqueous gypsum slurry, which after setting represents a positive mold of the mouth. In recent years, silicones of both the condensation cure and addition cure varieties have become widely used as impression materials. They exhibit very good accuracy, together with an absence of taste and odor, easy demolding and other properties generally equivalent to or better than other commonly-used impression materials. However, silicone impression materials suffer from the disadvantage of hydrophobicity. This causes inaccurate impressions in moist fields, and discourages thorough wetting and accurate replication when the model is poured. In an attempt to provide better wetting of the impression by the gypsum slurry, some dental laboratories spray the cured impression with a detergent solution just prior to pouring the model
Repeated attempts have been made to render silicones more hydrophilic by chemically modifying the siloxane backbone or by appending to the backbone various functional groups. Typical approaches are described in U.S. Pat. Nos. 4,259,467 (and in many of the references cited therein) and 4,332,922.
Siloxanes have been used as surface active agents, emulsifiers, defoamers or coatings, see, e.g. U.S. Pat. Nos. 3,057,901, 3,398,104, 3,402,192, 3,505,377, 3,560,544, 3,929,509, 3,980,688, 4,160,776, 4,226,794, 4,337,168, 4,395,454, 4,414,660, 4,431,789, 4,468,491, 4,510,227, 4,517,240 and Re. 25,727. Other publications describing the properties of siloxanes include "Silwet.RTM. Surface Active Copolymers" (product literature from Union Carbide Corp., dated October, 1983), "Organomodified Oils [OMO]"(product literature from Union Carbide Corp., dated April, 1982), "UCARSIL.RTM. EPS Silicone Hydrophilic Finish" (product literature from Union Carbide Corp., dated March, 1984), "Silicate Cluster.TM. Fluids (product literature from Olin Corp.), and Vick, S.C., "Structure/Property Relationships for Silicone Polyalkyleneoxide Copolymers and Their Effects on Performance in Cosmetics", Soap/Cosmetics/Chemical Specialties, 60 (5), 36 (May, 1984).
U.S. Pat. No. 4,354,873 describes an antifouling coating for application to submerged boat hulls. The coating contains fumed silica, silicone oil, antifoulant, and an anionic, nonionic or amphoteric surfactant.